1. Field
The present invention relates to a method and its apparatus for the separation of butene-1 from a C4 hydrocarbon mixed gas including butene-1, trans-2-butene, cis-2-butene, normal butane, isobutane, etc. by using a hybrid process composed of an adsorption process and a distillation process.
2. Description of the Related Art
The known method for the separation of butene-1 from a C4 hydrocarbon mixed gas including C4 olefins (butene-1, trans-2-butene, cis-2-butene, ct.) and C4 paraffins (normal butane, isobutane, etc) involves mainly a distillation process. However, the known method requires the use of distillation towers with a large number of fractionation plates due to the small boiling-point difference of the products to be separated and thus leads to high consumption of energy and to high investment costs.
TABLE 1Boiling point of the C4 hydrocarbon mixtureComponentsMolecular weightBoiling point (° C.)Isobutane58.124−11.7Isobutene56.108−6.9Butene-156.108−6.31,3-Butadiene54.092−4.4Normal-butane58.124−0.5Trans-2-butene56.1080.3Cis-2-butene56.1083.7
U.S. Pat. No. 4,718,986 (1988) discloses a process for producing butene-1 of more than 99 wt % from the C4 hydrocarbon mixture of butene-1/isobutane/normal butane/butene-2 by using two distillation towers. According to the above patent invention, the C4 mixture is introduced into the first distillation tower to remove isobutane from the top of the tower. The lower stream from the first distillation tower is introduced into the second distillation tower, obtaining butene-1 with a purity of 99 wt % from the top of the second tower and discharging a mixture of normal butane, butene-2 and butene-1 from the bottom of the second tower. However, since a considerable amount, of butene-1 is discharged with the isobutane stream from the top of the first tower and also with the mixture of normal butane, butene-2 and butene-1 from the bottom of the second tower, the above process results in much loss of butene-1.
There are a number of known techniques relating to the adsorption-separation processes for a C4 hydrocarbon mixture, for example, a technique for separating butene-1 from a mixture including butene-1/butene-2/isobutylene by using type X or Y zeolite containing potassium ion or barium ion (U.S. Pat. No. 3,723,561, Mar. 27, 1973), a technique for separating butene-1 from a liquid C4 hydrocarbon mixture by using type K—X zeolite (U.S. Pat. No. 4,119,678, Oct. 10, 1978), a technique for separating normal C4 hydrocarbon mixture and isobutylene by using a molecular sieve selective to normal C4 hydrocarbon mixture (U.S. Pat. No. 4,455,445, Jun. 19, 1984), a technique for selectively separating alfa olefin alone from olefins having more than 4 carbon atoms by a liquid adsorption process using a zeolite molecular sieve (U.S. Pat. No. 5,132,485, 1992), a pressure-swing adsorption process for the separation of olefins/paraffins having 2-6 carbon atoms in vapor phase by using type 4A zeolite (U.S. Pat. No. 5,365,011, 1994), and a technique for separating paraffins from a mixture of olefins/paraffins having 2-6 carbon atoms in vapor phase using type X or Y zeolite and reproducing the adsorbents used in the adsorption process by using desorbents (BP 0708070 81, 1999). The U.S. Pat. No. 5,955,640 (1999) discloses a process of improving the yield of butene-1 by converting butene-2 components into butene-1 while removing a portion of paraffin components by using an adsorption process in order to prevent the accumulation of unreacted paraffin components in the process.
However, distillation using two towers connected in series as shown in the above U.S. Pat. No. 4,718,986 (1998) is the only process used for obtaining butene-1 with high purity from the C4 ole fins/paraffins mixture gas. Till now, there is no adsorptive-separation techniques that can separate butene-1 with high purity from a mixture of C4 olefins/paraffins by selectively separating C4 olefin mixture gas from C4 olefins/paraffins mixture by an adsorption process and then obtaining high purity butene-1 from C4 olefin mixture gas selectively separated from the adsorption process by a distillation process, as can be achieved by the present invention.